[Hampshire] xorg.conf problems in new Etch install

X is insisting on running at 640x420 and 60Hz. My monitor optimally
requires 1280x1024 @ 75 Hz. I have tried to edit xorg.conf, but can see
nothing wrong with it, apart from a wrong attribution of screen - but teh
settings look all right. Here below are the relevant lines. Please, can
anyone suggest a fix? I already know that K(U)buntu misrecognises the
screen inthe same way. Obviously I could reinstall Libranet 3 and update it
ot Sarge again, but that doesn't seem sensible at this stage. But all
suggestions sympathetically listened to.

TIA
Lisi

Section "Device"
        Identifier      "nVidia Corporation NV18 [GeForce4 MX - nForce GPU]"
        Driver          "nv"
        BusID           "PCI:2:0:0"
EndSection

Section "Monitor"
        Identifier      "PLE431"
        Option          "DPMS"
EndSection

Section "Screen"
        Identifier      "Default Screen"
        Device          "nVidia Corporation NV18 [GeForce4 MX - nForce GPU]"
        Monitor         "PLE431"
        DefaultDepth    24
        SubSection "Display"
                Depth           1
                Modes           "1280x1024" "1152x864" "1024x768" "832x624"
"800x600" "720x400" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           4
                Modes           "1280x1024" "1152x864" "1024x768" "832x624"
"800x600" "720x400" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           8
                Modes           "1280x1024" "1152x864" "1024x768" "832x624"
"800x600" "720x400" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           15
                Modes           "1280x1024" "1152x864" "1024x768" "832x624"
"800x600" "720x400" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           16
                Modes           "1280x1024" "1152x864" "1024x768" "832x624"
"800x600" "720x400" "640x480"
        EndSubSection
        SubSection "Display"
                Depth           24
                Modes           "1280x1024" "1152x864" "1024x768" "832x624"
"800x600" "720x400" "640x480"
        EndSubSection
EndSection

Section "ServerLayout"
        Identifier      "Default Layout"
        Screen          "Default Screen"
        InputDevice     "Generic Keyboard"
        InputDevice     "Configured Mouse"
EndSection

Section "DRI"
        Mode    0666
EndSection